I just picked up two of the 150 gal sized bins from a closing store, they were doing what you have planned, I will be doing the same, though with external pumps. I will have my media in large garbage cans, they will sit on top of the bins instead of down in them. So depending on how full they are I will have a bit of splashing where the water exits the garbage cans but it shouldn't be too bad.
As for dividing them, best way I can think of is create brackets and mount them inside of the bins to the walls and the bottom, then slide the light diffuser down into it. It should stay pretty sturdy if mounted well. I'd think some good silicone should stick well.
As for dividing them, best way I can think of is create brackets and mount them inside of the bins to the walls and the bottom, then slide the light diffuser down into it. It should stay pretty sturdy if mounted well. I'd think some good silicone should stick well.